This invention relates to a rotationally-molded refuse container with an integrally-molded handle sealed from communication with the refuse compartment of the container. Rotational molding provides advantages not present in other molding processes, such as blow-molding and injection molding. Rotational molding generally provides economical tooling costs, one-piece, stress-free and light-weight construction, uniform wall thickness, the ability to produce multi-wall and complex hollow parts and to include metal inserts as integral parts, products with resistance to stress-cracking and corrosion, and the ability to design products with minor undercuts without draft angles being required.
Rotational molding takes place by melting a thermoplastic resin, such as polyethylene or polypropylene powder or pellets, in a biaxially-rotating, heated mold. The interior shape of the mold corresponds generally with the shape of the product to be molded. The particles of thermoplastic resin melt and puddle in the bottom of the mold. As the mold is rotated simultaneously through a vertical and horizontal axis, all parts of the mold rotate through this puddle of thermoplastic resin, causing a thin layer of the material to coat the inner surface of the hot mold surface and fuse to the mold in layers. The process continues with the fused layers becoming progressively thicker until the desired product thickness is achieved and the layers have taken on the shape of the mold being used to form the product. A principal characteristic of a typical rotationally-molded product is that it is hollow. The thickness of the walls of the molded product is controlled by the amount of powder and/or pellets with which the mold is charged before the biaxial rotation of the mold begins.
After the all of the charge has melted and fused to the interior walls of the mold, the mold is moved to a cooling chamber where the mold is cooled by air, water or a mist of the two. The part in the mold cools to the point where the mold can be opened and the part removed.
Rotational molding must be carefully distinguished from blow molding. In general, the blow molding process is carried out by extruding a hollow, tubular-shaped, thermoplastic preform, referred to as a "parison", from an extrusion machine into the interior of an open mold. The walls of the mold are then closed and a gas, such as air, is blown into the mold and into the preform. The expansion of the gas under pressure causes the preform to expand and move outwardly against the interior walls of the mold. The shape of the interior walls of the mold define the shape of the product to be molded, and the thickness of the product can be controlled by controlling the shape and size of the parison. Protrusions, which may be internal or external to the body of the product being molded, provide strength and rigidity to the product. Wall thickness and distribution of the material throughout the product is controlled by the shaping of the extrusion die. Blow molding molds can have moveable segments which pinch off pieces of the parison and form it into solid forms, which can be used for reenforcing areas of the product or providing greater rigidity. It is also possible to pinch off areas in such a way as to create enclosed voids in the product being molded. This permits a considerable increase in strength while minimizing weight gain.
Rotational molding does not lend itself quite so easily to the formation of enclosed voids. By definition, full and even fusion of the thermoplastic material to the inner walls of the mold requires that all areas of the mold be open to being coated as a particular part of the mold passes through the puddle of molten thermoplastic material.
This application presents a processing step which permits a hollow area to be closed off from adjacent hollow areas by a solid wall, while nevertheless providing full opportunity for all areas of the mold to be properly coated with thermoplastic material during the molding process. In the example provided in the application, a hollow handle of a roll-out refuse container is sealed off from the refuse compartment.